1. Field of the Invention
The present invention relates to an on-chip balun, a transceiver using the same, and a method for fabricating the on-chip balun, and more particularly, to an on-chip balun having a phase imbalance and a gain imbalance, a transceiver using the same, and a method for fabricating the on-chip balun.
2. Description of the Related Art
Base stations and radio stations use radio frequency (RF) transmitters including balanced and unbalanced transmission lines in wireless networks for use with receivers such as pagers, mobile phones, personal digital assistants (PDAs), or the like. In general, a Balanced-to-Unbalanced network (balun) is used to couple a balanced circuit to an unbalanced circuit. In other words, the balun converts an unbalanced signal into balanced differential signals and outputs the balanced differential signals. Also, a balun having an on-chip form is often used to match impedances between amplifiers.
FIGS. 1A through 1C are views illustrating a conventional transformer balun. FIG. 1A is a cross-sectional view of the conventional transformer balun, FIG. 1B is a view illustrating a first winding 35 of the conventional transformer balun, and FIG. 1C is a view illustrating a second winding 25 of the conventional transformer balun.
Referring to FIG. 1A, the conventional transformer balun includes the first and second windings 35, 25 sequentially formed above a first insulator 11. A second insulator 13 is formed between the first insulator 11 and the second winding 25, and third and fourth insulators 15, 17 are formed between the first and second windings 35, 25.
Referring to FIGS. 1B and 1C, one of two ports of the first winding 35 formed on the fourth insulator 17 is grounded, and an unbalanced signal is input to the other port. A magnetic field is induced around the first winding 35 due to a current flowing in the first winding 35, and induced current flows in the second winding 25 due to the induced magnetic field. Since an intermediate point of the second winding 25 is grounded, a current output from one of two ports of the second winding 25 and a current output from the other one of the two ports of the second winding 25 have the same intensity but have a phase difference of 180°. Here, the first and second windings 35, 25 are symmetric.
However, a parasitic capacitance occurs between the first and second windings 35 and 25 of the conventional transformer balun. Here, the parasitic capacitance occurring between the first and second windings 35, 25 is an asymmetrical parasitic capacitance causing two differential signals converted in the second winding 25 to be asymmetrical. Thus, a signal having a phase imbalance and a gain imbalance is generated in the conventional transformer balun. In other words, a phase difference between differential signals generated at the two ports of the second winding 25 is not 180°, and the differential signals have different intensities.
FIG. 2 is a view illustrating another conventional transformer balun. Referring to FIG. 2, the conventional transformer balun includes a substrate 50, an insulating layer 60, a first winding 70, and a second winding 80 formed on the first winding 70.
The conventional transformer balun shown in FIG. 2 is different from the conventional transformer balun shown in FIG. 1 in that the first wining 70 is positioned underneath the second winding 80, and the first and second windings 70, 80 are asymmetrical. A port of the first winding 70 is grounded, and an unbalanced signal is input to a port 71 of the first winding 70. Here, a ground line may be formed by forming a viahole in an insulating layer (not shown) formed between the first and second windings 70, 80. Also, an intermediate point of the second winding 80 is grounded, and thus currents flowing through first and second ports 81, 83 of the second winding 80 have the same intensity but have a phase difference of 180°.
However, in such a conventional transformer balun, an asymmetrical parasitic capacitance occurs between the first and second windings 25, 35. Thus, a signal having a phase imbalance and a gain imbalance is generated in the conventional transformer balun.